The present subject matter generally concerns a broadband antenna with load circuits and matching network, and more particularly concerns a broadband monopole antenna with parallel inductor—resistor load circuits. The subject loaded antenna design may be optimized by various tools including a genetic algorithm and integral equation solver.
Wire antennas have been used in countless communications applications, and often require the ability to provide omnidirectional capabilities over a wide range of frequencies. Many basic antenna configurations exist that radiate in azimuth with omnidirectional capabilities, such as a wire monopole antenna or dipole antenna. However, these types of antennas are typically characterized as narrowband. In order to increase the bandwidth of such antennas, load circuits can be added at regular intervals along a general wire antenna segment. Such load circuits may comprise a selected combination of passive elements, including resistors, inductors and/or capacitors.
Another potential method for increasing the bandwidth of monopole or dipole antennas is to include a matching network at the base of the antenna where it is driven to the ground plane. Such a matching network ideally matches the impedance of an antenna to that of the transmission line or other medium to which it is connected. Numerical results for a loaded monopole antenna having a matching network are presented by K. Yegin and A. Q. Martin in “Very broadboand loaded monopole antennas,” IEEE AP-S International Symposium Digest, vol. 1, pp. 232-235, July 1997, Montreal Canada.
Given a general antenna configuration, various methods are known that can optimize specific parameters corresponding to the configuration. For instance, parameters corresponding to a loaded monopole antenna may include the values of passive elements used in the load circuits, the position of load circuits along an antenna arm, and the values of elements used in matching networks. There are several tools known in the field of antenna design that are available for optimizing such parameters. These tools include genetic algorithms and integral equation solvers.
Genetic algorithms (GAs) are robust search and optimization routines which simulate the theory of evolution on a computer in order to maximize or minimize a user-defined objective function. An initial set of candidate antenna configurations are presented and evaluated in terms of an objective function. Better antenna configurations are allowed to reproduce into further generations of additional antenna configurations. The generation process may typically account for crossover between generations or mutations to randomly selected designs. A GA typically performs multiple iterations of this generation process to yield a set of antenna configurations with optimal solutions to the defined objective function. An example of the type of genetic algorithm used is embodied by a FORTRAN program developed by David Carroll, details of which are presented by D. L. Carroll in “Chemical Laser Modeling with Genetic Algorithms,” AIAA Journal, vol. 34, no. 2, pp. 338-346, February 1996.
Genetic algorithms and the numerical equations incorporated therein to model loaded antenna configurations typically model the load circuits as lumped elements concentrated at a node. This may not be the best way to model a load circuit, especially if the load circuit comprises passive elements that have a larger diameter than the antenna arm to which the load circuits are added. An example of genetic algorithms with lump load modeling used to design optimum antenna configurations is presented by Alona Bag et al. in “Design of Electrically loaded wire antennas using genetic algorithms,” IEEE Transactions on Antenna Propagation, vol. AP-45, pp. 1494-1501, October 1997. Only theoretical configurations and numerical results are presented.
It is desired to readily construct such a loaded monopole antenna that works well over a broad range of frequencies. Such a configuration could potentially replace several antennas that operate in different frequency bands. A single functioning loaded monopole is desired for applications requiring such broadband operation, such as in conjunction with basestations or vehicles in a mobile communication network. The construction and realization of such loaded monopole/dipole antennas with matching networks is thus desired.
The disclosures of all of the foregoing technical references and journal articles are hereby fully incorporated for all purposes into this application by reference thereto.